The present invention relates to a wavefront aberration measuring instrument for measuring a wavefront aberration of a target optical system such as a projection optical system in an exposure apparatus used in a photolithography step in a manufacturing process of a micro device such as a semiconductor element, a liquid crystal display element device, an image pickup element or a thin-film magnetic head, a wavefront aberration measuring method, an exposure apparatus having the wavefront aberration measuring instrument, and a method for manufacturing the above-described micro device.
There has been conventionally known an exposure apparatus which illuminates an image of a pattern formed on a mask, such as a reticle or a photo mask, with exposure light and transfers the image of the pattern onto a substrate such as a wafer or a glass plate on which a photosensitive material such as a photoresist is applied through a projection optical system.
In recent years, integration of semiconductor elements has become increasingly higher, and a demand for realization of the finer circuit pattern is increasing. In order to meet this demand for realization of the finer circuit pattern, there has been developed an exposure apparatus using a far ultraviolet ray with a shorter wavelength, for example, pulse light such as a KrF excimer laser beam (λ=248 nm), an ArF excimer laser beam (λ=193 nm) or an F2 laser beam (λ=157 nm).
Further, in order to meet the demand for the finer circuit pattern, aberration measurement of the projection optical system is carried out for the purpose of optimization of an image formation performance of the projection optical system. Aberration measurement of the projection optical system is carried out as follows, for example. That is, a mask for aberration measurement is arranged on a surface of an object, an image of a predetermined pattern formed on the mask is baked on the substrate arranged on the image surface of the projection optical system, and the baked image is developed. Then, a magnifying power, a degree of asymmetry property or the like of the developed image is measured by using a scanning electron microscope (SEM), and an aberration of the projection optical system is obtained based on the measurement result.
However, the prior art method has a problem that the accuracy of measuring the aberration can not be sufficiently assured due to a manufacturing error of a pattern of the mask for aberration measurement, irregularities of application of the photoresist, a processing error of development unevenness or the like. Further, in observation using the SEM, a predetermined pretreatment for the substrate, for example, a development process or the like of the substrate is required, and it takes a long time for measuring the aberration.
In order to avoid such a problem, there is considered a method of measuring the aberration of the projection optical system as a wavefront aberration based on, for example, Shack-Hartmann system. In this system, spot light which is image-formed on an image forming surface of the projection optical system is converted into a parallel beam by a collimator lens. Then, the parallel beam is caused to enter a micro lens array having many lenses two-dimensionally arranged. As a result, the parallel beam is image-formed on an image pickup element arranged at a predetermined position for each lens.
Here, when no aberration exists in the projection optical system, each lens of the micro lens array forms an image of the incident light flux on an optical axis of each lens since the parallel beam entering the micro lens array has a parallel wavefront.
On the other hand, when the aberration exists in the projection optical system, the parallel beam has an inclination of the wavefront which differs from lens to lens since the parallel beam entering the micro lens array has a distorted wavefront according to the aberration. Furthermore, the light flux which has entered each lens of the micro lens array is image-formed at a position deviating from the optical axis in accordance with an amount of inclination of the wavefront for each lens. The inclination of the wavefront can be obtained from the image formation position for each lens.
However, in the prior art method, the wavefront aberration measurement unit including the collimator lens, the micro lens array and the image pickup element is arranged at, for example, a predetermined position on a substrate stage which supports the substrate, and the wavefront aberration of the projection optical system is measured by using this wavefront aberration measurement unit in this state. At that moment, a detection surface of the wavefront aberration measurement unit must be arranged in the image formation surface of the projection optical system.
If the detection surface is not arranged in the image formation surface of the projection optical system, not only a defocus component is increased but the accuracy of other aberration components may be possibly decreased when wavefront aberration information obtained by measurement using the wavefront aberration measurement unit is developed to various kids of aberration components by using, for example, a polynomial equation of Zernike.